Bar type or linear displays have been in use for many years in instrumentation for presenting data to an operator, as an alternative to circular gauges using needles, or alpha-numeric displays. Bargraph displays emulate vertical or horizontal bars, the length of which represents the level of an input to the instrument. It is also known to create an alarm such as a separate light or sound when an input value exceeds a limit.
In modern instrumentation, the mechanical bar has been replaced with an array of electronically controlled lights of a single color, arranged in a series of illuminatable segments adjacent to markings corresponding to input values. Devices of this type and their distributors or manufacturers include: the Universal Bargraph, by the Triplett Corporation, One Triplett Drive, Bluffton, Ohio; Solid State Analog Panel Meters, by Bowmar/ALI, 531 Main Street, Acton, Mass.; and Vibration Monitors, by PMC/BETA Corporation, 4 Tech Circle, Natick, Mass. Alternatively, the illuminated segments have been arranged in linearly displaced groups, each group having a fixed color to identify the different significance of the values in the different groups. This limits the points of change to fixed values. A device of this type is disclosed in U.S. Pat. No. 4,874,253 to Pompei et al. Some of the devices have supplemental alpha-numeric displays which compliment the bargraphs by displaying additional information which the limited prior art devices are unable to accommodate.
A common flaw in all of the prior art bargraphs is their limited capability to clearly present warning or danger information in a single display. In prior art bargraph displays, the existence of an input which exceeds a value or represents a warning may only be represented by a single LED illumination which cannot be seen at a distance.